Free tool · Law Enforcement
Stop or Arrest? Reasonable Suspicion and Probable Cause Explained
Under US constitutional law, a police encounter falls into one of three levels. A consensual encounter, where a reasonable person would feel free to leave or decline, needs no suspicion. A brief investigative stop (a Terry stop) is a seizure that needs reasonable suspicion based on specific, articulable facts that criminal activity is afoot, and must be limited in time and scope. An arrest needs probable cause, a fair probability that the person committed a crime. Handcuffs, a long detention or being taken to the station can turn a stop into a de facto arrest. A frisk of outer clothing in a lawful stop needs a reasonable belief that the person is armed and dangerous. A hunch is never enough. State law and department policy may demand more.
Tool · Encounter Level Finder
An investigative stop (a Terry stop), supported on these facts.
Requires: Reasonable suspicion
Type of encounter: A brief detention to check whether crime is afoot is a seizure that needs reasonable suspicion of criminal activity. It must be limited in time and scope to what is needed to confirm or dispel the suspicion.
Level of suspicion: The officer had reasonable suspicion, which is enough for a stop.
- A hunch is not enough for any seizure. Reasonable suspicion must rest on specific and articulable facts, judged on the totality of the circumstances (Terry v Ohio). Probable cause is a fair probability that a crime has been or is being committed, or that evidence will be found.
- The categories are the federal constitutional floor. State constitutions, statutes and department policies often demand more, and an unlawful seizure can lead to suppression of evidence (the exclusionary rule), subject to exceptions.
Classifies a police-citizen encounter on invented facts as a consensual encounter, an investigative stop, an arrest or a warrant seizure, shows the suspicion each requires and tests whether the officer’s facts support what was done, including a frisk. It states the federal constitutional floor in simplified form; state law and policy may demand more. A teaching aid, not legal advice. Runs in your browser; nothing is stored or sent.
How to use it
- Say whether the person was free to leave and how they were restrained.
- Choose the level of suspicion the officer actually had.
- Tick any warrant, move to the station or frisk.
- Read the type of encounter and whether the facts support it.
Common questions
What is the difference between reasonable suspicion and probable cause?
Reasonable suspicion is a lower standard based on specific facts suggesting criminal activity, enough for a short stop. Probable cause is a fair probability that a crime was committed or evidence will be found, needed for an arrest or a warrant.
When does a stop become an arrest?
When the restraint goes beyond a brief detention to confirm or dispel suspicion: for example, prolonged detention, handcuffing without need, or transport to the station.
What happens if the stop was unlawful?
Evidence obtained may be suppressed under the exclusionary rule, subject to exceptions such as good faith, inevitable discovery and attenuation.
Learn the law behind the tool
This tool is part of our Law Enforcement course, with lectures, concept maps, flashcards, interactive exercises and a capstone case. Law Enforcement: Police Authority and the Fourth Amendment.
More free law tools
General information, simplified, mainly on American law, not legal advice. States and countries differ, and real cases turn on facts that a tool cannot capture.